Field of the Disclosure
This disclosure generally relates to a heat exchanger unit with characteristics of improved: airflow, noise reduction, cooling efficiency, and/or structural integrity. More specifically, the disclosure relates to a heat exchanger unit used in connection with equipment found in an industrial setting. In particular embodiments, the heat exchanger unit may be used for cooling various utility fluids used with a heat generating device, such as an engine, a pump, or a genset.
Background of the Disclosure
Whether its refrigeration, hot showers, air conditioning, and so on, the function of heating and cooling is prevalent in today's residential and industrial settings. One area of relevance is the oil and gas industry, including exploration, upstream, and downstream operations where the ability to heat and/or cool is critical. Upstream operations can include drilling, completion, and production, whereas downstream operations can include refining and other related hydrocarbon processing, all of which utilize a vast amount of process equipment including that which provide heat transfer.
As the modern world continues to experience growth in population, it similarly continues to experience an increase in energy demand and consumption, and the oil and gas industry needs to respond accordingly. Although ‘green’ energy has experienced a gain in popularity, the dominant source of energy remains fossil fuels. Driven by demand and high prices for fossil fuels, the U.S. energy sector experienced a boom in the late 2000's and into the early 2010's, contributing to expansion in exploration and production across the country.
Quite unexpectedly various global economic factors resulted in a rapid turnaround in demand and a decrease in profit margin that left many industry related companies vying to remain in business. This has resulted in consolidation and innovation, as the reality of likely never again seeing the record highs associated with the price of oil sets in. To remain competitive, companies have begun looking at how they can be successful and profitable with a margin based on an oil price in a range of about $30-$50 per barrel.
A particular segment in the upstream area of oil and gas production pertains to fracing. Now prevalent, fracing includes the use of a plug set in a wellbore below or beyond a respective target zone, followed by pumping or injecting high pressure frac fluid into the zone. The frac operation results in fractures or “cracks” in the formation that allow valuable hydrocarbons to be more readily extracted and produced by an operator, and may be repeated as desired or necessary until all target zones are fractured.
The injection fluid, which may be mixed with chemicals, sand, acid, etc., may be pressurized and transported at high rate via one or more high pressure frac pumps, typically driven by diesel combustion engines.
FIGS. 1A and 1B together illustrate a conventional land-based fracturing operation and frac pump trailer unit. The operation 101 may include multiple frac pump units 105. Each unit 105 is typically operable with a pump 113 and engine 103 mounted or otherwise disposed thereon, and is capable of producing upwards of 15,000 psi. Suitable units 105 include those manufactured or provided by NOV, Haliburton, Magnum, Weatherford, and the like. See http://www.nov.com/Well_Service_and_Completion/Stimulation_Equipment/Fracturing_Pump_Units.aspx.
The necessity of fracturing has progressively increased as production rates on new wells continue to decline. It is believed by some that at least 90 percent of all future wells in North America will require some degree of fracturing to increase production results, with a majority of these operations occurring in shale gas formations.
As demand continues to rise, producers have moved to unconventional sources such as the Barnett Shale, which for the first time resulted in wide reliance on horizontal drilling, leading to an increase on pumping pressures and operating times. Horizontal drilling and its associated multistage fracturing techniques are now the norm as shale formations have become the leading source of natural gas in North America. This harsher pumping environment demands stronger pumps capable of operating at extreme pressures and extended pumping intervals.
The frac pump is now part of a pumping system (or skid unit, etc.) that is typically self-contained on a transportable system, such as a trailer unit 105. The system components include the engine 103 and the frac pump 113, as well as a radiator (or cooler, heat exchanger, etc.) 100. Today's pumps are capable of producing 2500 BHP @ 1900 rpm while operating in standard pressure pumping well service operations in ambient conditions of about 0° F. to 125° F., and can provide upwards of 15,000 psi injection pressure at a working rate of 17 bpm. The frac pump 113 provides pressurized fluid into well(s) 191 via transfer (injection) lines 190.
But there are several drawbacks to this modern equipment. First, the operational requirements have driven the associated equipment to become massive in weight, and single trailer units sometimes exceed 80,000 lbs. Unfortunately the trailer unit 105 must comply with federal, state, and local regulation, where a number of regulators are starting to draw a line on weight limitations. Permits for a job site will only be issued when requirements are met.
Similarly, the operational requirements have driven the associated equipment, such as the diesel engine or radiator fan, to become huge point sources of noise pollution. And again, regulators are starting to draw a line on noise. This is even more problematic as job sites start to encroach closer and closer to residential areas.
Next, operational requirements have driven the associated equipment, for example the diesel engine, to become extreme generators of heat, thus requiring a larger cooling system. The typical radiator further adds significant weight to the trailer unit. And as a result of spatial constraints, the radiator 100 often lies horizontal on the bed of the trailer unit 105, as shown in FIG. 1B. The problem with this arrangement is that as the radiator fan 108 blows in ambient air to cool various service fluids (F1, F2, F3, etc.), the air becomes progressively hot (e.g., cooling in series, where Tout>T2>T1>Tamb). See FIG. 1C. This temperature gradient results in ineffective cooling as the air is moved through the radiator 100.
The heat exchanger is typically used to cool by passing a hot service fluid through the heat exchanger along one path (or side), and passing a cooling medium through the heat exchanger along a second path (or side). In an air-cooled radiator, a fluid may circulate through the equipment and pass through the first side, and air may be drawn through the second side to cool the fluid before it returns to the equipment.
Operational requirements have further attributed to extreme conditions (e.g., temperature, pressure, vibration, etc.) that subject equipment to additional failure modes, for example, it has been found that leaks may occur at the joints of the equipment.
One type of heat exchanger is one that may be formed from a series of header bars and face bars, with plates connected between the bars to form flow paths. One or more tanks may be connected in fluid communication with either or both of a first and a second path to direct fluid flow through the respective path. In one example, in which plates are brazed to the header and face bars, and tanks welded to the ends of the heat exchangers, it was found that leaks were occurring adjacent to the header and face bars.
It was found that when the header bars and face bars were small, the heat affected zone related to a weld between the core and the tank extended past the header bars and face bars and into the brazed joint between the plates and the respective bar(s). When the weld temperature (i.e., melting point of weld material) was greater than the brazing temperature, the brazing material would melt and flow away, such that the connection at these points was either opened, or weakened, and resulted in greater likelihood of failure during operation.
FIG. 1E shows a close-up side view of part of a radiator core. A tank 177 is welded to the core 106 at the core end 106a (i.e., the weld point). The tank 177 has a tank end, which has an effective tank end mass. The mass of the tank (and its end) 177 is extensive (including as depending on tank wall thickness Wt), and a significant amount of heat must be applied in order to reach the weld temperature Tw at the weld point. The temperature of the melting point of the weld material Tw (typically about 1200 F) is greater than the melting point Tb (typically about 960 F) of the brazing material between the parting sheets 172 and respective bars 175 (e.g., header and face). As the tank end mass of the tank end (Mte) is larger than a core end mass of the core end (Mce), the presence of weld temperature at the weld point results in a heat profile P into the core 106 (which the profile P may be parabolic).
Heat at the weld point radiates along the easiest path. As the heat profile of temperature greater than Tb extends length l, and is beyond the effective bar brazing length (or area A) 185 of the bar 175, the brazing material B (by having a melting temperature Tb less than weld temperature Tw) is heated and can freely flow or leach away from the area A between the bar 175 and the parting sheet 172. This results in the core 106 being susceptible to failure because upon cooling the brazing is now incomplete.
Another issue that reduces the structural integrity of the heat exchanger unit is the thermal expansion of a radiator core, particularly those made of aluminum. Typically a core is rigidly mounted without regard for how it might expand in application. However, as the core experiences expansion, it becomes prone to leaking. It was determined that a cause of the leaks was the impact of thermal expansion, with some large heat exchangers expanding by almost ½″. As the cores are solidly brazed together and then hard mounted (welded or nut/bolt) to a frame, the stress from expansion caused cracking in some welds due to excessive load being applied to it.
Thermal expansion occurs, for example, when the radiator core is manufactured at ambient temperature, but is generally exposed to temperatures well above ambient during use. As a result, the material of the core will expand. As the core is normally rigidly mounted to a support structure, which resisted thermal expansion, it is believed that stresses are induced in the heat exchanger, and that failures can occur in the welds as a result.
One or more of these concerns is just as valid to non-oilfield related heat exchangers. FIG. 1D illustrates a simple schematic overview of a heat generation device (HGD) 103a used in a general industrial operation or setting 101a. The operation or setting 101a may be a construction site, a building, a water treatment plant, a manufacturing facility, or any other setting whereby a heat exchanger 100a is used for heat transfer, such as to cool (or heat) a utility fluid F that is used with the HGD 103a. The operation of a fan 108 results in an undesirable noise characterized by an acoustic frequency f with amplitude A1, which his readily discernable to an operator.
In an analogous manner HGD's associated with a residential setting may also have similar concerns. In other aspects, it is becoming more and more common that an industrial setting or operation is adjacent or proximate to a residential setting.
There is a need in the art to overcome deficiencies and defects identified herein. There is a particular need in the art for a heat exchanger that is readily adaptable and compatible to different pieces of heat generating equipment, such as an engine, a motor, a pump, or a genset useable in a wide range of settings.
There is a need in the art to be able to reduce pressure drop, whereby airflow through a heat exchanger can be streamlined and increased. There is a need to reduce sound emission from a heat exchanger so that it may satisfy regulatory limitations or be suitable for use in or proximate to a residential setting.
There is a need in the art for a heat exchanger that can accommodate spatial constraints, and is lighter in weight. There is a need in the art for a heat exchanger that has improved or reduced sound emissions. There is a need in the art for a heat exchanger that improves cooling efficiency. There is a need in the art for a heat exchanger with improved structural integrity, including the ability to withstand or tolerate thermal expansion and hot welding temperatures.